1. The Field of the Invention
This invention relates to translucent and/or transparent polymer-based panel assemblies that incorporate colors through applied colored film layers.
2. Background and Relevant Art
Laminated translucent panel systems have achieved a wide utility in designed architectural assemblies and applications, as well as lighting and display applications. One of the main facets of significant interest is the ability to add color to such panel systems. Translucent panel systems come in a variety of forms and assemblies ranging from composites to products produced from polymers to glass. Traditional means of achieving color with the aforementioned substrates are through paints and coatings, dye and pigment concentrates or dispersants, or through adhesion of colored films, fabrics or papers. Many of the aforementioned coloring systems introduce aesthetic, performance or manufacturing constraints when combined with the aforementioned polymer-based or glass-based panel systems.
One category of methods to achieve a colored translucent or transparent thermoplastic panel is through direct application of color through screen printing or painting. With screen printing, ink is applied to the surface using traditional screen printing methods. Drawbacks of screen printing include the fact that the ink may be scratched off of the panel surface. In addition, the ink typically needs to be bonded to the panel with bonding additives that are often solvent-based and often produce undesirable volatile organic compound (VOC) emissions.
Painting is another way of applying color to the surface of a panel. Like screen printing, paint may also be scratched from the surface of the panel. Additionally, painting, and more particularly cleanup from painting, also results in undesirable VOC emissions. Moreover, colors or images applied through screen printing or painting are only correctly viewable from one side of the panel. Also, panels colored or decorated using these methods tend to require cure times of between four and twelve hours, during which time the panels require special storage and possibly drying units.
A second category of methods for achieving a colored translucent or transparent thermoplastic panel is through the infusion of color into the surface of the panel. One method of this category is dye sublimation printing, during which solid sources of dye, such as a printed transfer paper, are heated, placed in contact with a receiving substrate and the printed color or image is transferred to the substrate and subsequently cooled. This method results in the color or image penetrating the substrate such that it is more resilient to surface scratches. Moreover, the colors or images produced using this method may be viewed equally well from either side of the panel. The dye sublimation method, however, requires considerable technical expertise to create the digital master files and an understanding of the interaction of the dye with the substrate. Dye sublimation is also a capital-intensive operation that tends to require specialized printing equipment.
A second method in this category for infusing color into a translucent or transparent thermoplastic panel is by driving pigment into the surface chemically. For example, one conventional mechanism includes bombarding the surface of a thermoplastic panel with solvent that temporarily improves the solubility of the panel, thereby allowing dyes carried in the solvent to be transferred—and incorporated in—the matrix of the thermoplastic panel. Although this method is not entirely capable of rendering a predetermined image, the color driven into the surface of the panel in this way does yield a homogeneous color, and is more resilient to surface abrasion than colors applied directly through screen printing or painting.
Unfortunately, this chemical process consumes large amounts of energy. The final quality also tends to be quite dependent on several process variables and strict process control. The cycle time, and the regulation of temperature and solvent concentration are driving forces that determine the quality of the finished panel. In addition, the equipment required to employ this method is very costly. Furthermore, it takes a significant amount of time to change over between one color and the next because the system must undergo a cleaning cycle to flush out each color after use.
A third category of means for imparting color to a translucent or transparent thermoplastic panel is through the use of a fabric interlayer. Here, the method of imparting color to panels includes the use of colored textiles. Using colored textiles to achieve a uniform panel color, however, presents several challenges. One challenge is that fabric has a texture of its own that remains visible through the translucent or transparent thermoplastic panel. In addition, while colored textiles may be used selectively to control the translucency of a panel, they tend to impair the transparency of a panel.
Moreover, thermoplastic panels with textile interlayers are not generally suitable for wet environments without additional fabrication precautions, because the fabric at the exposed edges of the panel will wick moisture into the interior of the panel. This wicking action through the fabric layer introduces color distortion and staining within the panel. In addition, the viewability of color or an image depends upon whether the color or pattern is woven into the fabric or printed on only one side of the fabric. Also, fabric interlayers interfere with recycling because they can not be easily separated from the resin substrate.
Furthermore, if more than one fabric interlayer is used, the most visible color will be that of the textile layer nearest the viewer, since colors are not blended or mixed when using textiles. In addition, care must be taken when laying up fabric interlayers because if they are not placed straight and taut, the fabric layer can create the appearance of waves. Still further, multiple layers of fabric may create the moiré effect, which can be further exaggerated depending on the thickness of any substrate interposed between fabric layers. Another consideration when constructing thermoplastic panels with fabric interlayers is that the fabric layer may not be on the surface. Moreover, care must be taken to ensure that the fabric layer is laid up in the center of the overall panel thickness to create a “balanced lay-up.”
Otherwise the panel, once constructed, will bow as it cools, and the bowing is an undesirable characteristic. Also, fabric layers within panels reduce the ability to thermoform the panels since the fabric will separate or pull away under deep draw conditions due to the physical limitations of the fabric. A last disadvantage of fabric layers within panels is that the fabric may wick moisture into the body of the laminated panel if edges are exposed to wet environments.
A fourth category of technology for coloring a translucent or transparent thermoplastic panel is through the use of films or “sheets” colored during manufacture with compounded pigments and dyes. In general, a “sheet” refers to that portion of a translucent polymeric resin panel which, in its prefabrication state, is a unitary extrusion of material, typically measuring 2-6 feet wide and 8-12 feet long, and at least 1/32 of an inch in thickness. By contrast, a “film” refers to a thin, membranous layer with the same planar dimensions as a sheet but with a thickness ranging from 0.001 mils to 30 mils, but preferably 0.5 mils to 20 mils, and most preferably 10 mils.
There are conventional mechanisms and apparatus that involve using colored films or sheets to create colored panels. Unlike panels constructed with embedded fabric layers, such conventional mechanisms involve no texture that is visible in panels formed with colored films. In addition, according to one conventional technology, such panels must be constructed with two co-polyester sheets, and include a backing layer, which backing layer may also be colored. Accordingly, with this technology, there are at least two interfaces where air entrapment can be a problem.
In addition, panels constructed for high-relief surfaces, when incorporated with a fabric or a printed or a colored image, may experience wrinkling of the fabric or unusual distortion of the color or image when captured between a top layer that is heavily textured and a back layer. The assembly may further require a laminating enhancing layer (LEL), in addition to thermally compatible surfaces, to achieve bonding and to facilitate the removal of air between the adjacent layers. Removal of air from the panels is important, since any air pockets that remain in a finished panel can create a notch or point of weakness with the laminate matrix that can result in crack propagation and failure in notch-sensitive thermoplastic materials. Applying a laminating enhancing layer tends to require additional processing steps, and increases material costs and introduces potential for contamination. In addition, the laminating enhancing layer must be uniformly applied for best results. Furthermore, the laminating enhancing layer, whether an actual film or a sprayed-on material, is not generally the same material as the substrate. Similar to fabric interlayers mentioned above, this dissimilarity contributes to the inability of such panels to be reclaimed and recycled because the dissimilar resin material would be a contaminant in the recycling stream for the panel substrate which constitutes the majority of the panel.
A drawback of using colored films or sheets under the conventional art is that, typically, colored films are produced in large quantities to achieve economies of scale. As a result, the customer must purchase a large quantity of a single color or image in order to obtain favorable pricing. This is compounded by the need to purchase multiple colors in order to offer a variety of color choices. Such high-volume purchase requirements can lead to unnecessary expense due to inventory obsolescence. Alternatively, a purchaser may purchase small quantities of custom colored films at a much higher price for less than full-run quantities. As alluded to above, the sheets forming the substrate of the panel may themselves be colored with pigments or dyes by introducing color to the raw material during the process of sheet manufacture. Here again, economies of scale apply, requiring the purchaser to purchase high volumes of colored sheets to obtain favorable pricing or to pay extremely high prices for small quantities of custom colors.
As introduced earlier, there are a number of conventional mechanisms that involve the use of laminated translucent resin panels with a decorative image layer with or without a laminating enhancing layer. In such cases, the decorative image layer is a printed or colored film layer wherein at least one of the film layer's surfaces is colored or has an image printed thereon. In addition, the decorative image layer only occurs between outer layers. Moreover, a laminating enhancing layer may be a required element to ensure adhesion of the various dissimilar layers and to facilitate removal of air from between them. Incorporating a laminating enhancing layer not only increases the processing steps and materials required, but also, such additional inputs can increase the potential occurrence of manufacturing defects or contamination within the laminate. Because the laminating enhancing layer is non-homogeneous, it typically must be carefully tested and applied to ensure that proper coverage is attained for bonding to occur. Such conventional mechanisms use a backing layer, which can overcome the increased level of defects caused by the additional processing requirements, but, in the process, further increase the processing requirements. Furthermore, the backing layer may or may not be of optical quality, and could reduce the transparency or translucency, or both, of the resulting panel.
There are still other conventional mechanisms, which use colored films produced from polyvinyl butyral (“PVB”) for use in glass lamination. According to such mechanisms, the colored PVB layer is used as a tie-layer to facilitate lamination of multiple glass layers. Such mechanisms, however, are usually specifically directed toward laminated glass compositions.
In addition, colored PVB films, while necessary in the laminated glass composition, may contain plasticizers, which may not be compatible with certain thermoplastics such as the copolyester known as PETG, (i.e., polyethylene-co-cyclohexane 1,4-dimethanol terephthalate), polycarbonate, or acrylic (e.g., polymethyl methacrylate, or PMMA). Furthermore, PVB tends to require special handling and storage conditions including refrigeration. Such requirements can add expense to the use of PVB in laminations. Also, plasticizers used in PVB are known to craze polycarbonate when used in laminations with polycarbonate.
Ethyl vinyl acetate (EVA) films are known to provide good bonding characteristics for laminated glass structures. Such films are available in a variety of colors from such companies as Sekesui; however, such films are not ideal for use on the surface of panels due to the fact that they attract dirt and debris, making them difficult to use. The surface tends to be very sticky and has a low surface roughness, which often requires that a vacuum be used to remove air during lamination. Further, EVA has a limitation if used to construct interior architectural paneling applications due to its relatively high flammability.
As noted above, an inherent challenge in manufacturing laminate panels is avoidance of the tendency of the panels to retain air between the layers unless preventative measures are taken to remove the air. Examples of methods used in the art for this purpose include the use of a laminating enhancing layer and/or vacuum bagging, and using an autoclave to remove the air. Use of laminating enhancing layers and/or vacuum bagging, however, requires additional lay-up and processing steps and materials, all of which increase expense.